Our laboratory is interested in the role of endogenous serotonin as it relates to gut transport and motility. We have extensive experience with a rat colon model, and plan to expand our work as follows: 1. We will characterize the release and transport response to endogenous 5-HT released via mucosal stimulation. 2. Based on the information learned using rat colon preparations we will delineate the function of physiologic 5-HT on human jejunum using novel isolated perfused tissue model. 3. Concurrently, we will study the effects of physiologic 5-HT on rat bowel transport and motility using an in situ animal model.